After a fashion, that might be by intent. They told us how the chicken is butchered--not the eleven herbs and spices, so to speak.
4e is designed in such a way that it is VERY CLEAR what a class is supposed to be. When you start designing one you would be pushed to define its thematics and core mechanics in terms of role and power source immediately. From there you develop class features to express those along with the 'concept' of the class (that you will have to come up with yourself) and then create powers, feats, PP, and ED perhaps, etc. to go along with that. Its generally not a solo sort of thing if you want success. I'd point out that WotC employed many people to do this work, and the results were almost entirely consistently really good stuff.
Contrast this with 3e classes, about 90% of which are, frankly, garbage. Nope, 4e is a regular class design KIT, it just doesn't promise that the work will be easy, when in fact it never is.
This is another perfectly valid criticism of 4e. Finding the right balance between fast and engaging combat is a difficult thing, and 4e erred on the side of slow (but definitely engaging) combat. Procedural adjustments can speed it up, as can back-end math changes (MM3), but a bit more effort could be put toward that goal. Trying to get most combats done in (say) 30-40 minutes as opposed to 45-60 minutes would be a big help; that would let a typical 3-4 hour session feature 3-4 combats and 1-3 hours of non-combat play.
Only if you are firmly fixed on just leaning on the tactical aspect of 4e and not the other aspects. I mean, I just don't do boring "you enter a room there are 4 orcs" kind of combats that people will complain about lasting an hour. MOST of the ones I do are really dynamic, and only incidentally involve one side wiping the other side out completely. Definitely seen some fights break down into a less fun mode, but I hate to tell you that every other D&D has the same sort of problem. By the time we set up a 1e fight with minis and got all into it, you were almost surely burning an hour!
That's part of why, if I ever made a 4e heartbreaker, I'd put in what I call "Skirmish" rules. Rules for running really fast, low-engagement combats, that can capture the "fight five kobolds...several times" kinds of combat from earlier editions, while still providing meaningful stakes and conflict. Essentially, if full "social combat" rules would be like taking Skill Challenges and expanding them into a complete "social-tactical" experience, these proposed Skirmish rules would be like distilling down the combat engine into something like a Skill Challenge, fast, light, and flexible, but not as deep as proper combat rules. In the ideal case, "Skirmishes" would be satisfying enough on their own that you could effectively treat "Skirmish-only 4e" as the "Gygaxian Combat Module," sort of the logical opposite of the vaporware "Tactical Combat Module" that the 5e designers promised.
I thought about this, and I wrote such rules even, but they just didn't prove to be compelling at all. Like, just have some minions show up and don't even fight it out is better. Let the party make a low complexity SC to see if they take a couple surges worth of damage. ANOTHER resolution system just seemed one too many, but that's just me, go for it!
Runepriest becoming a subclass of Cleric, Seeker to Ranger, and...what, exactly? Eliminating those two leaves 23 classes. Just by keeping the thirteen found in 5e you're already more than halfway to keeping all of the remaining 4e ones (13/23). Swordmage, Avenger, Warden, and Shaman are all really cool, so I'm not sure if we can justify cutting them; that's 17/23. I never cared for the non-Monk Psionic classes, the whole design around Power Points and Augment abilities is deeply flawed, but just axing them seems like such a waste. That leaves Assassin, Invoker, and Vampire; Assassin has plenty of history (it was even a class in 3e!), so that seems to be out too, but perhaps you want it gone. Where would Invoker go--Wizard? Holy magic seems incredibly out of place for a Wizard, but diluting Cleric by building a whole separate controller side into it seems just as bad. Vampire is some really cool design, but I guess we could ditch it....and in so doing, we'll only have gotten rid of 2 (obvious picks: Runepriest/Seeker) + 3 (Augment-based classes) + 3 (Assassin, Vampire, Invoker) = 8 classes. That's still 17, and with some painful sacrifices to get there.
Well, Binder can simply go away. It was a nothing both thematically and mechanically, definitely the closest to a 'fail class' in 4e. I've personally no use for the e-classes either, several of which are virtually worth nothing IMHO. I'm not SURE where your 23 comes from, I count 22 full classes between three PHBs, and then there are the ones from the settings, Swordmage, Artificer, and then post-Essentials has Vampire, and then there are some heavily variant subclasses like the Skald and the Berserker, which technically aren't classes, but kinda are, as well as the Bladesinger, which definitely is, though it steals its powers from Wizard. There's also the Elementalist, which is another pretty variant 'build' of Sorcerer. Finally we have 2 Assassin classes. So AT LEAST 28, and I'm not even counting the Binder in that, or the Blackguard, which is a pretty variant paladin.
Now, I'm happy to ditch psionics, which gets rid of three, Seeker is OK, but we could live without that. Runepriest is very fiddly and thematically seems like a cleric, and we can do without the post-e classes, except the Vampire, which rocks. I think that gets us to 19 classes that I would consider ones I don't want to give up. Yes, there are some that not everyone thinks are very thematic, like Invoker, but I bet those people haven't PLAYED an Invoker either! And I think some of the classes I just put on the block other people won't want to get rid of either.
It's all well and good to say "not all sources need all roles," but a number of these classes are actually fun on their own. As I previously argued, they aren't just "grid filling." They were made to work with the lore, have fun and engaging mechanics all their own, and actually have meaning and purpose, not just rote performance. There are diehard Warden fans out there, even though many who didn't enjoy 4e would just write it off as "oh that's a Barbarian played as a tank." I, personally, am a huge fan of Avengers even though I've never actually desired to play one, I just think they're neat. (I even built an entire "internal police" force for the main religion of my Dungeon World game, strongly inspired by the lore of Avengers.) Vampires may be kind of superfluous/overly-specific, but they have an incredibly neat mechanic in their tiny pool of healing surges and need to extract surges from the enemies they face. Etc.
Warden's kick butt, and they are thematically NOTHING like barbarians! Just wait until your warden uses 'Form of the Walking Conflagration' lol, or 'Form of the Stone Sentinel'. I remember when my group's Warden powered THAT little gem up. Yeah, the heck with all your high damage bad guys, I'm just going to stand here and not care! lol.
These things aren't pointless. That means you actually have to start saying that some stuff just doesn't belong in 4e if you want to axe any meaningful set of classes.
And this is, more or less, my response to a lot of requests for mass reduction of stuff in 4e. It's very easy to talk about "oh just cut stuff in half!" It's a hell of a lot harder once you actually sit down and start asking what is such a problem that it merits being cut. That's sort of the problem with 4e being actually well-designed. A lot of its components are actually really good, and ditching them solely for simplicity's sake becomes a lot harder to justify. Feats and powers are the main exception, because a lot of them are just poor, but they don't fit into neat boxes--you have to actually review them. Much like how probably half or more of the spells in 5e aren't actually all that good or worthwhile, but the only way to winnow the wheat from the chaff is to actually review the spells.
Yeah, I think you CAN do a pretty serious trim on Feats, but you WILL have to basically rewrite 4e to cut back much else, or else really rip out a lot of extremely good content! Also, who cares if there are 9000 powers? Honestly, what difference does it make? Your character only needs like 10 of them right now. Feats are a bit harder question, because you really do end up milling through a LOT of feats every couple levels.